voyeur:

1. Paraphilic individual, more often a male, who derives sexual gratification from observing unsuspecting people, almost always strangers, undressing or engaging in sexual-behavior ; the risk of discovery heightens the pleasure. The voyeur will usually masturbate during or after the peeping . This definition includes people who watch themselves and their partner during sex . Voyeurs generally have a history of insecurity and fear of rejection .They rarely approach or harm their victims; there has been very few reports of rape associated with voyeurism .